1. Field of the Invention
The present invention relates to a fabrication method for a semiconductor device and a manufacturing apparatus for the same.
2. Description of the Related Art
In order to improve large scale integrated circuit (LSI) performance, the integrated density or miniaturization of the elements used to configure an LSI has been enhanced. In order to miniaturize elements, reduction in the area of an impurity diffusion region as well as formation of a shallower diffusion region along the depth of the diffusion are required. For that purpose, it has become important to optimize ion implantation, which forms an impurity diffusion region such as a source and a drain region and a functional region such as a channel region just beneath a gate insulator layer, and the subsequent annealing process.
This annealing has been performed under conditions of, for example, 1000 Celsius (° C.) for 30 minutes. With such high-temperature and lengthy annealing time, impurity diffusion has occurred in addition to activation of impurities. In order to solve this problem, annealing should be performed for a minimum period of time to activate impurities with little diffusion. For example, rapid thermal annealing (RTA) using a tungsten (W) halogen lamp annealing under conditions of 1000 Celsius for approximately 10 seconds has been adopted. In recent years, a desired impurity profile cannot be obtained, since impurity diffusion occurs even after performing the annealing for a short time.
Therefore, adoption of a laser annealing method has been considered as a method of instantaneously providing a sufficient energy density required for activation. However, since a laser light inherently has high coherency and directivity, a multiphoton process or interference may occur. In addition, the original laser light has an energy density per time and per area that is too high. As a result, the surface of a silicon semiconductor substrate may melt or evaporated, or laser ablation may occur. Therefore, the morphology of a surface layer of a semiconductor substrate will be deteriorated after activation.
A flash lamp annealing (FLA) method using a flash lamp that includes gas such as xenon has been spotlighted as a means of improving the activation rate of impurities in an extremely short time in addition to the RTA or the laser annealing. Flash lamp annealing conditions are, for example, an electrical conduction time of 10 msec or less and an irradiation energy density of 100 J/cm2 or less. FLA has received attention as a new annealing method that can control and activate impurity diffusion simultaneously without causing any secondary deteriorating effects as with the laser annealing.
A method of annealing a wafer to a specific temperature using a first lamp such as a halogen lamp, and then irradiating and annealing that wafer using a second lamp such as a flash lamp, that is, a method of annealing a wafer using two types of lamps, each of which lights for a different irradiation time, has been suggested as described in Japanese Patent Application Laid-Open No. 2002-151428. In addition, a method of performing a first lamp annealing process with higher energy density than the band gap of an amorphous semiconductor film, and performing a second lamp annealing process with an energy density greater than the band gap of a monocrystal semiconductor film and less than the band gap of an amorphous semiconductor film, that is, a method of changing a lamp wavelength according to the band gap of a semiconductor layer has been disclosed as described in Japanese Patent Application Laid-Open No. 2000-260710.
Miniaturization of elements and reduction in element dimension are important results of formation of a shallow source and a drain diffusion region or a shallow source and a drain extension diffusion region. As a method of doping impurities to a shallow region, both ion implantation at low acceleration energy density and subsequent short-time RTA processing have been adopted. Nevertheless, once the RTA processing is performed even only for several tens of seconds after ion implantation of boron (B), which is conventionally used as the p-type dopant, and phosphorus (P) or arsenic (As) as the n-type dopant, diffusion may occur deep in the substrate since a silicon (Si) substrate has a high diffusion factor. In addition, when the annealing temperature is reduced, there is a problem that the activation rate of impurities drastically declines. Accordingly, it is difficult to form a shallow impurity diffusion layer with a junction depth of less than 50 nm and with low resistivity.
In recent years, the above-mentioned FLA has been spotlighted as a means of improving the activation rate in an extremely short time. Employment of FLA allows control of impurity diffusion and formation of an extremely shallow junction. However, with FLA which performs annealing in a matter of milliseconds, it is difficult to sufficiently fix crystal defects, which are developed in the semiconductor substrate during the ion implantation process. Immediately after the ion implantation process, a crystal structure in a region where dopant is implanted in the semiconductor substrate is partially damaged and turns into an amorphous layer. This amorphous layer must be re-crystallized with, for example, subsequent annealing. If a large amount of crystal defects remain in, for example, the source and the drain region, those crystal defects may develop into a conductive path. This may cause an increase in leakage current during transistor operation, resulting in deterioration in the characteristics. On the other hand, in the case of annealing with RTA, annealing is performed at least for several seconds. If that annealing is performed until reaching the temperature capable of activating impurities, for example, 1020 Celsius, the high temperature is maintained for at least several seconds and a heat energy density sufficient for re-growth of crystals can be obtained. Therefore, the crystal defects can be fixed. However, in this case, it is difficult to form a shallow junction since the impurities will deeply diffuse.